The present invention relates to core substance-containing calcium microparticles and methods for producing the microparticles.
As a core substance to be enclosed by the method of the invention, any substance may be selected. For example, the core substance may be one of table luxuries, seasonings, flavoring agents, vitamins, drugs, antibiotics, physiologically active substances, or microorganisms. Thus, the present invention can be used in various fields such as the food industry and pharmaceutical industry.
In drugs and a group of foods called "health foods" (e.g. functional foods from natural sources), some of them are physically and/or chemically unstable; some of them have a bitter taste or offensive smell; and some of them are easily degraded in the stomach.
As a method for stabilizing such substances during storage or in the digestive tract and facilitating oral administration of drugs or health foods with a bitter taste or offensive smell, various means have been employed including enclosure into capsules, combination of flavoring/aromatic agents, and various coatings (sugar coating, enteric coating, etc.). However, since capsules and coated tablets are relatively big in size, some individuals feel difficulty in taking them; they are not absorbed well; and it is difficult to use them as a raw material for preparing processed food.
Toward the solution of the above problems, the present inventors have found that it is possible to enclose an oily physiologically active substance with solid microparticles by utilizing the following principle. Briefly, when an oily physiologically active substance is added to water and agitated at a high rate to form an o/w emulsion, the oil droplets in the emulsion behave as a sort of solid; as a result of relative movement with the water, .zeta. potential is generated on the surface of the oil droplets and they are electrostatically charged; under this state, if solid microparticles are added which are smaller than the oil droplets and which bring about an electric charge opposite to that on the oil droplet surface, the solid microparticles are adsorbed on the oil droplet surface. Also, the inventors have found that calcium particles are preferable as the solid microparticles. Thus, the inventors have already filed a patent application for the above findings (Japanese Unexamined Patent Publication No. 7-328416).
However, if the core substance of the microparticles is unstable, sometimes the inherent properties of the core substance may change due to temperature, pH, agitation rate and the passage of time. Thus, the selection of the core substance was restricted. When the core substance is water-soluble, the substance easily elutes into the water. phase during the manufacturing process, causing a problem that its enclosure is extremely difficult or impossible.
Further, although the oily physiologically active substance-enclosing microparticles disclosed in Japanese Unexamined Patent Publication No. 7-328416 mentioned above have acid resistance, they do not have a function to regulate the dissolution rate of the core substance. Thus, it was difficult to apply those microparticles to drugs and the like which are required to maintain their efficacy in the body for a long period of time.